Rheostat



(No Model.) Bf-Shets-Sllleet 1.

W. THOMSON. RHEOSTAT.

No. 420,894-l Patented Feb. 4, 1890.A

N. gk .5

n. rnsngmL-mnpw. wmp u. c.

('NoModel.) 3 Sheets-Sheet 2.

W. THOMSON. RHBOSTAT.

No. 420,894. Patented Feb. 4, 1890.

N PETERS. Phomlimnamnnr. wnshmglon. D, c.

(No Model.) 3 Sheets-Sheet 3.

W. THOMSON. RHEOSTAT.

No. 420,894. Patented Feb. 4, 1890.

CID

n. rimas, www-ogm. vla-mmm. n. c.

UNITED rSTATES PATENT OFFICE.

VILLIAM THOMSON, OF GLASGOV, COUNTY OF LANARK, SCOTLAND.

RH EOSTAT.

SPECIFICATION forming part of Letters Patent No. 420,894, dated February 4, 1890K.

Application filed October 4, 1888, Serial No. 287,153. (No model.)

T0 au whom, it may concern:

Be it known that l, WILLIAM THOMSON, knight, doetorot laws and professor of natural philosophy in the University and Oollege of Glasgow, of Glasgow, in the county of Lanark, Scotland, have invented an Improved Rheo'stat, of which the following is a specification.

This invention relates to an improved form of VVheatstones rheostat. The rheostat consists of wire, preferably platinoid, wound on two cylinders. To adjust the resistance of the rheostat continuously to any desired amount, the wire of the instrument is guided from one cylinder to the other by a :fork earried through the requisite range by a nut traveling on a long screw-shaft. The screwshaft carries a toothed wheel which turns two cylinders by means of toothed wheelsatta ehed to their shafts. A watch-spring, as in J olins improvements oi' Vheatstones rheostat, keeps the wire always tightened to the proper degree. A leather butter at each end of the range of the nut acts as a guard againstoverwinding in either direction. The rheostat is worked by the hand to any extent necessary so as to keep the current constant.

In the drawings, Figure l is a front elevation of Wheatstones rheostat arranged according to my improvements. Fig. 2 is an end elevation of the same. Fig. 2 is a detail View ot' the two cylinders. Fig. 3 is a plan thereof.

Referring t0 these drawings, a screw-shaft 3'2, provided at oneend with a convenient handle 71:2, has a toothed wheel Z2 fixed to it and in gear with twov toothed wheels m2 a2, fixed, respeetivel v,to the shafts of two cylinders o2 and p2. One of these cylinders is fast on its shaft and the other is connected with its shaft through a coiled spring, which by its pull on the cylinder serves, as in .Tolins improvement of lVheatstones rheostat, to keep the wire q2 tightened round the cylinder. (See Fig. 2U One of the cylinders presents a lsmooth in sulating-covering. When the screw-shaft l7'2 is turned, the wire is guided from one cylinder to the other by means of a fork or a small wheel r2, carried by a nut s2. The nut is prevented from turning when the shaft is turned by a guide-fork t2, which slides along the edges of a scale u2 and carries a Vernier for indicating the position of the nut on the screw. The currentcircuit through the wire passes from a terminal 122 through a iiexible spring 202, pressing against the end of a stud a2 in contact with one end of the wire, and from the wire it passes to a stud 'y2 to another Iiexible spring 52, and through it to the other terminal a3. A guard-washer b3, of leather or other suitable substance, (placed at each end of the screw jt) prevents overwinding in either direction' by limiting the travel of the nut s2.

I claiml. The combination of the cylinders 02232, the guide t2, guide-roller r2, and a nut s2, carrying the guide and guide-roller, with a screwshaft jg, on which the nut travels, said shaft being geared tothe cylinders and the nut being prevented from rotating, substantially as herein described.

2. The combination of the cylinders carrying the wire, the screw-shaft geared to the cylinders, the nut carrying the guide and mounted on the screw-shaft, and the bar ai, said nut having the forks engaging the bar, whereby the nut is kept from turning, as explained.

3. The combination of the cylinders, screwshaft, guide-nut, and guide-fork with the scale-bar engaged by the fork and adapted thereby to indicate the position of the nut, as explained. f

at. The combination of the cylinders carrying the wire, screw-rod carrying the nut and gearing with the cylinders, and the guideroller r2, located on the nut, for the purpose explained.

5. The combination of the rollers, screw, nut., and bar u2 of the fork t2 on the nut engaging the bar, said bar having a scale and the fork having a vernier, for the purposes herein explained.

In testimony whereof I have signed my name to this specification in thc presence of two subscribing witnesses.

WILLIAM THOMSON. Witnesses:

Sr. JoIIN V. DAY, J oIIN LIDDLE, l 50th of 115 St. Vincent Street, Glasgow. 

